© Levi Cowan/TropicalTidbits.comTropical/subtropical cyclone tracks in the Pacific Ocean, according to the IBTrACS database.
An exceptionally rare subtropical storm appears to have formed off the central coast of Chile in the southeast Pacific Ocean, typically one of the world's most tropical cyclone devoid ocean basins.
The subtropical cyclone formed late last weekend several hundred miles west of the South American coast.
The advanced scatterometer aboard the EUMETSAT satellite found the system had
a well-defined surface low,
with winds of 40-45 mph and
shallow thunderstorm activity surrounding but not in its center Tuesday.
These ingredients define the system as a subtropical storm, a system with characteristics of both a conventional tropical cyclone and a colder, non-tropical low-pressure system you may see over land or water in the middle latitudes.
This system formed in water temperatures between 64 and 68 degrees, which is usually not supportive of sufficient thunderstorm activity that would help build a subtropical or tropical cyclone.In this case, as with many subtropical cyclones of this nature, it had some atmospheric support. This cyclone is in the midst of an upper-level trough, or cold pool, of low pressure, adding the instability needed for thunderstorms.
This system is spinning clockwise, typical of any storm in the Southern Hemisphere, as both high-pressure and low-pressure systems spin in the opposite direction as they do in the Northern Hemisphere.
Interestingly, if there was a cyclone season in that part of the world, this system would have nearly fallen outside of it. A cyclone in the southern Pacific occurring in May is like a tropical storm occurring in November in the Atlantic. If there was a peak month for activity surrounding South America, it would be in February or March, so this system is quite late.
How Rare Is This?It may be one of a kind. No other recognized subtropical or tropical storm has been documented in that part of the world.
Comment: For details of the earlier storm, see: Powerful 'freak' dust storms kill over 125 people in north India, highest death toll in decades - UPDATES